1. Field
The present disclosure generally relates to vacuum bag processing of composite parts, and deals more particularly with a vacuum bagging method using a stretchable vacuum bag assembly that conforms to contoured surfaces of the parts.
2. Background
Composite laminate parts may be cured using autoclave or out-of-autoclave processes. These processes typically employ a combination of heat and pressure applied by a vacuum bag to compact and consolidate the part. A breather may be placed between the part and the vacuum bag in order to allow escape of air and volatiles from the laminate, and thereby avoid undesired entrapment of these gases.
Curing composite laminate parts and adhesives using the processes mentioned above presents a number of challenges where a part has certain geometries and/or surface contours such as inside radii. For example, breathers may have difficulty in conforming to an inside radius on the part, resulting in what is commonly referred to as “bridging”, in which the breather and overlying vacuum bag bridge over the area of the radius. Bridging may have the undesired effect of reducing the local compaction pressure that is applied to the part. One partial solution to the problem of bridging, is to apply the breather in multiple pieces that are individually hand-placed around a surface contour where bridging may occur. Alternatively, the use of breather material in contoured part areas may be completely avoided, however the absence of a breather in these areas may limit the ability of air and volatiles to escape from the laminate. Multiple piece breathers are labor intensive to cut and install, and result in material scrap. In some applications, the lack of a breather in areas of the part where bridging is probable may result in inadequate breathing of these areas.
Another challenge presented in vacuum bag processing of parts with certain geometries involves the placement and positioning of the vacuum bag over the breather. During the bagging process, bulk vacuum bag material is draped over the part and is loosely hand fitted to the general geometry of the part. The bagging process usually results in local accumulations of excess bag material in some areas of the part. This excess bag material is gathered together and hand formed into pleats. It is often necessary to meticulously form these pleats at precise locations on the part in order to reduce bridging of breather materials during curing. For example, in the case of a part having multiple inside radii, a pleat in the bag material must be hand formed at the exact location of each of these radii. The presence of a bag pleat at a radius area allows the bag to expand into the radius and maintain compaction pressure in the radius area. However, the need to hand form each pleat in the bag material is time consuming and labor intensive. Moreover, the use of a bag pleat in a radiused area of the part may not reduce bridging of the breather material to the desired extent.
Accordingly, there is a need for a method of vacuum bag processing contoured composite laminate parts that reduces or eliminates undesired bridging of vacuum bag materials, and reduces labor and material costs. There is also a need for a vacuum bag assembly that is capable of conforming to surface contours, such as an inside radius of a part, and which may be quickly and easily installed.